Jacketed gasket



March 23, 1965 c. M. HOBSON, JR 3,174,764

JACKETED GASKET Original Filed July 20, 1959 Fig.

Fig. 2; *M i t\\\ \V/ /A No x United States Patent 2 Claims. or. 277-231This invention relates to gaskets of the type having jackets offluorocarbon resin and has for an object the provision of gaskets andthe method of manufacturing the same in which the outer fluorocarbonresin surface has been modified and rendered non-slippery. Thoughapplicable to gaskets having outer surfaces of polytetrafluoroethyleneavailable on the market under the trademark Teflon, the invention canalso be used in regard to gaskets having an outer surface ofpolychlorotrifluoroethylene available on the market under the trademarkKel-F.

Teflon and Kel-F resins have characteristics which make the materialsquite valuable for gaskets and par ticularly suitable for jacketedgaskets. Such resins are stable at high temperatures and chemicallyresistant to acids and other corrosive substances except fluorine atelevated temperature and molten sodium. By reason of thesecharacteristics, gaskets having an outer layer or covering of Teflon orKel-F have become extremely important for use in chemical piping andassociated equipment. Many of these gaskets are used in applicationsinvolving the joining of glass-lined steel equipment, piping and thelike which in itself provides a very slippery surface. Teflon and Kel-F,being such slippery materials when utilized in contact with the slipperyglass surfaces, require excessive bolt-loading pressure on the jointswhich frequently damages the glazed lining, resulting in expensiverepairs. This condition is due specifically to engaging highanti-friction surfaces and another cause of faliure because of thiscondition is the shifting of the gasket during installation. Further,under high vacuum service, this condition has caused the jacket to bepulled completely into the vessel or pipeline.

All of these conditions are of a critical nature and it has been foundthat they can be minimized or eliminated in accordance with the presentinvention.

The present invention is particularly applicable to a pipe joint or thelike having flanges which have a slippery or low friction surface. Afluorocarbon resin gasket is disposed between the flanges with the facesthereof in engagement with the slippery surfaces. The gasket ischaracterized by the faces being of a fluorocarbon resin which has beenrendered non-slippery to increase the frictional resistance of thegasket with respect to the pressure within the pipe. Further inaccordance with the invention there is provided a jacketed gasketconstruction including a pair of opposed outer surfaces ofpolytetrafluoroethylene or the like, such surfaces being modified toincrease their coefiicient of friction and render them non-slippery.

Further in accordance with the invention, there is provided a method ofmaking a fluorocarbon resin jacketed gasket with non-slippery surfacesincluding the steps of forming a strip of fluorocarbon resin tape into aclosed ring with the ends of the tape in abutting relation, welding theabutting ends of the tape together to form an endless ring, treating atleast the inner surface of the ring of tape with a solution of anhydrousammonia and metallic sodium to modify the surface and render itnon-slippery, and forming the endless ring of a tape around an innergasket of resilient material with the modified non-slippery surfacebeing exposed to provide the opposed surfaces of the jacketed gasket.

ice

This application is a division of parent application Serial N0. 828,366filed July 20, 1959, which is directed to the provision of a jacketedgasket in which the jacket is made from Teflon or Kel-F tape which hasbeen buttwelded to form an endless ring and thereby eliminate thecondition of double thickness and non-uniform thickness of the gasketjacket normally found in conventional lapwelded joints.

For further objects and advantages of the invention and for a moredetailed disclosure thereof, reference is to be had to the followingdescription taken in conjunction with the accompanying drawing in which:

FIG. 1 is a top plan view of a jacketed gasket embodying the presentinvention;

FIG. 2 is a sectional view taken across the butt-welded portion of thejacket as indicated by lines Z-2 in FIG. 1;

FIG. 3 diagrammatically illustrates the manner of buttwelding the endsof the tape to form the jacket into an endless ring; and

FIG. 4 is a sectional view of a joint between two flanged sections ofglass-lined pipe with the gasket of FIG. 1 inserted therebetween.

Referring to FIGS. 1 and 4, the gasket ltl includes an outer layer orjacket 11 of fluorocarbon resin in the form of polytetratluoroethylenetape or equivalent. The tape is relatively thin, for example in theorder of .015" thick. The length and width of the tape required to formthe jacket 11 will depend upon the size of the joint which is to receivethe gasket. The gaskets, when completed, are in ring form and it is notunusual for them to have an CD. as great as 60 inches.

To form the tape into a jacket for the gasket, the tape is first cut toproper length and folded lengthwise along the center thereof into aU-shape as shown by the cross section of the jacket 11 in FIG. 4. Thelongitudinal edges of the tape are then pressed away from the centerfold, as by tapered rollers to stretch the tape along the edges and thuscause the folded tape to form into a ring with the ends thereof inabutting relation. The tape is then unfolded at the ends and the endsplaced in abutting relation for welding.

As indicated in FIG. 3, the ends of the tape 11 are butt-welded by theconcurrent application of heat and pressure. This has been schematicallyillustrated in FIG. 3 by the upper and lower pressure blocks 12 and i3which are heated by suitable means, such, for example as the heatresistor elements 14 and 15, the latter being energized from a suitablesource, not shown. It will be noted that the pressure blocks 12 and 13have a width sufficient to extend a substantial distance on either sideof the abutting ends of the tape 11. With this arrangement, the ends ofthe tape will be tightly welded together as indicated at area x in FIG.2 with only a small reduction in thickness of the tape at that area.This is particularly de sirable since it provides an endless ring orjacket 11 for the gasket which is substantially uniform in thicknessthroughout the entire circumference of the ring. This eliminates thecondition of double thickness and nonuniform thickness of the gasketjacket which is normally found in lap-welded joints and which presents asource of leakage when the gasket is assembled in a joint, such asillustrated in FIG. 4.

In welding the ends of the tape together to form the butt-weld, thetemperature utilized with Teflon is in the order of 700 F. (with Kel-F500 F.), the pressure is in the order of about 20 to 40 pounds persquare inch throughout the area of the blocks 12 and 13 and the pressureand temperature are maintained over a period of about one to twominutes, after which the welded area of the jacket is quenched in water.

After the jacket ill has been butt-welded into an endless ring, theinner surface thereof (i.e. the surface which,

surfaces 11a, it is dipped in a Washing tank to remove the excesssolution and then dried.

After the foregoing operations, the jacket 11 is then ready to beassembled about an inner gasket to form a completed gasket 19 as shownin FIGS. 1 and 4. The in-.

ner gasket may comprise a single ring of suitable resilient orcompressible material or it may comprise a plurality of rings. Forexample, as shown in FIG. 4, the inner gasket comprises a plurality ofrings 17, 18 and 19, the center ring 19 being illustrated as arelatively soft asbestos material While the outer rings 17 and 18 havebeen illustrated as a relatively hard compressed asbestos. It is to beunderstood that other inner gasket ringsmay be utilized such, forexample, as those of the type disclosed in my Patent 2,580,546.

The pipe joint illustrated in FIG. 4 is of the type in whichthe pipe 20and flanges 21 are provided with a glass lining 22. The flanges 21 areprovided with a series of holes extending around the periphery thereofthrough which a series of bolts 23 extend. The bolts 23 are providedwith nuts 24 which are adapted to be tightened.

until the loading on the gasket is sufiicient to retain it within itscentral location between the flanges 21, 21 and in axial alignment withthe mating pipe sections 20, 20. By reason of the non-slippery surfaceson. the jacketll, the bolt-loading pressure may be substantially reducedfrom pressures heretofore. required to retain the Teflon or Kel-Fgaskets in glass-lined pipe joints and other similar joints whichpresent slippery surfaces to the jacketed gaskets. It is believed thatthis substantial reduction in bolt-loading pressure is due to the factthat the static coefficient of friction for the Teflon or Kel-F surface,when treated in the foregoing manner, has been increased by at least inthe order of two. loading pressure to be decreased, the presentinvention has eliminated the danger of damaging the glass lining on thepipe and flanges due to overloading and has enabled the gaskets to bemaintained in their central position without shifting duringinstallation or during service under the application of high vacuum orother pressure conditions.

' It is to be understood that the present invention of treating Teflonand Kel-F gaskets to render their outer surfaces non-slippery is alsoapplicable to fluorocarbon gaskets of other types including the typesdisclosed in my aforesaid patent. It is further understood that the termBy enabling the bolt- 7 4- fluorocarbon resin employed in the appendedclaims is used generically and is intended to include Teflon and Kel-Fand their equivalents and that the term pressure is intended to includevacuum.

What is claimed is:

l. A gasket construction comprising an inner resilient compressiblesealing gasket and an outer. jacket of fluorocarbon resin enclosing saidinner gasket, said jacket comprising strip material of fluorocarbonresin with the ends thereof welded together in abutting relation toprovide continuous smooth unbroken exposed annular faces ofsubstantially uniform thickness throughout their circumferences, saidfaces having been rendered non-slippery to increase their coefficient offriction to a magnitude substantially above that of the normalcoefficient of friction of said fluorocarbon resin.

2. In a pipe joint between a pair of flanges at leastone together inabutting relation to provide continuous smooth unbroken annular faces ofsubstantially uniform thickness throughout their circumferences, saidannular faces having been chemically modified and rendered non-slipperyto increase their coefficient offriction to a magnitude substantiallyabove that of the'normal coefiicient of friction of said fluorocarbonresin thereby to increase the frictional resistance of said gasket withrespect to the pressure within said pipe.

References Cited by the Examiner UNIT ED STATES PATENTS 981,524 1/11Bonner 277207 2,459,720 7/49 Poltorak 277-227 2,580,546 1/52 Hobson277-231 XR 2,606,574 8/52 Lefebvre 285-55 2,705,693 4/55 Dildilian et a1156304 2,789,063 4/57 Purvis.

2,805,872 9/57 ROuth 285*55 2,898,229 8/59 Herr et al.

2,906,552 9/59 White 277-228 2,963,394 12/60 Wilkinson 156304 2,964,06512/60 I-Iaroldson et a1 13876 3,018,120 1/62 Vann 285-55 3,020,185 2/62Moflitt et al 277-229 XR 3,051,500 8/62 Wiltse 277228 EDWARD v. BENHAM,Primary Examiner. SAMUEL ROTHBERG, Examiner.

1. A GASKET CONSTRUCTION COMPRISING AN INNER RESILIENT COMPRESSIBLESEALING GASKET AND AN OUTER JACET OF FLUOROCARBON RESIN ENCLOSING SAIDINNER GASKET, SAID JACET COMPRISING STRIP MATERIAL OF FLUOROCARBON RESINWITH THE ENDS THEREOF WELDED TOGETHER IN ABUTTING RELATION TO PROVIDECONTINUOUS SMOOTH UNBROKEN EXPOSED ANNULAR FACES OF SUBSTANTIALLYUNIFORM THICKNESS THROUGHOUT THEIR CIRCUMFERENCES, SAID FACES HAVINGBEEN RENDERED NON-SLIPPERY TO INCREASE THEIR COEFFICIENT OF FRICTION TOA MAGNITUDE SUBSTANTIALLY ABOVE THAT OF THE NORMAL COEFFIOCIENT OFFRICTION OF SAID FLUOROCARBON RESIN.